Field of the Invention
The present invention relates to an inductor and an MMIC (Monolithic Microwave Integrated Circuit) used for a high-frequency device employed in a high-frequency radio device or high-frequency radar device or the like.
Background Art
Japanese Patent Application Laid-Open No. 2000-269418 discloses a spiral inductor with three layers of coil layered on one another. The coils of the first layer, second layer and third layer are formed in a spiral shape respectively. An air bridge is formed on the coil of the third layer to connect a central portion of the coil of the third layer and an outside of the inductor.
Coils may be formed in three layers to construct an inductor. An input terminal is connected to the coil of the bottom layer of the inductor and an output terminal is connected to the coil of the top layer of the inductor. When the coils of the three layers are formed in a spiral shape, a signal flows from an outside portion to an inside portion of the coil of the bottom layer, then flows from an inside portion to an outside portion of the coil of the intermediate layer and finally flows from an outside portion to an inside portion of the coil of the top layer. Therefore, connecting the coil of the top layer and the output terminal involves a problem that a complicated configuration such as the air bridge disclosed in Japanese Patent Application Laid-Open No. 2000-269418 is necessary. This problem exists not only in a case where coils are formed in three layers, but also in an inductor in which coils are formed in three or more odd-numbered layers (e.g., five layers).